1. Field
Example embodiments generally relate to fuel structures and materials used in nuclear power plants.
2. Description of Related Art
Generally, nuclear power plants include a reactor core having fuel arranged therein to produce power by nuclear fission. A common design in nuclear power plants is to arrange fuel in a plurality of fuel rods bound together as a fuel assembly, or fuel bundle, placed within the reactor core. These fuel rods typically include several elements joining the fuel rods to assembly components at various axial locations throughout the assembly.
As shown in FIG. 1, a conventional fuel bundle 10 of a nuclear reactor, such as a boiling water reactor (BWR), may include an outer channel 12 surrounding an upper tie plate 14 and a lower tie plate 16. A plurality of full-length fuel rods 18 and/or part length fuel rods 19 may be arranged in a matrix within the fuel bundle 10 and pass through a plurality of spacers 15. Fuel rods 18 and 19 generally originate and terminate at the same vertical position, all rods continuously running the length of the fuel bundle 10, with the exception of part length rods 19, which all terminate at a lower vertical position from the full length rods 18. An upper end plug 20 and/or lower end plug 30 may join the fuel rods 18 and 19 to the upper and lower tie plates 14 and 16, with only the lower end plug 30 being used in the case of part length rods 19.
As shown in FIGS. 2A and 2B, conventional upper and lower tie plates 14 and 16 may be generally solid and flat. A plurality of holes, called bosses, 25 may receive lower end plugs of all rods in an assembly in the lower tie plate 16. Similarly, a plurality of bosses 25 may receive the upper end plugs of all full-length rods in the upper tie plate 14. Part length rods may not terminate at a tie plate. In this way, upper and lower tie plates 14 and 16 may axially join fuel rods to the fuel assembly and hold fuel rods at a constant and shared axial displacement in the core. Because bosses and corresponding fuel rods may begin and/or terminate at the same axial position within the bundle, fluid flow may be restricted at these axial positions.
A continuing problem during operation of a nuclear reactor is the existence of debris of various sizes. Examples of such debris may include small-sized fasteners, metal clips, welding slag, pieces of wire, etc. The debris may be generated as a result of the original construction of the reactor core, subsequent reactor operation and/or due to repairs made during a planned or unplanned maintenance outage. Current fuel designs do not prevent particulate debris from entering the top of the fuel bundle. As work is performed during outages, there is the possibility that debris can enter the top of the fuel bundles and cause a fuel failure.